Alloy composition and process for the manufacture of glass making moulds

ABSTRACT

An alloy comprising: (i) 0.5-5 % by weight of one or more carbide formers selected from Molybdenum, tungsten and vanadium; (ii) 0.3 to 1.5 % by weight silicon; (iii) 5 to 40 % by weight chromium; (iv) 0.5 to 5 % by weight nickel; (v) 0.5 to 3.5% by weight boron; (vi) 0.1 to 0.5 % by weight of carbon; (vii) 0 to 2% by weight of manganese; (viii) 0 to 0.1% by weight of sulphur, (ix) 0 to 0-1% by weight of phosphorous; (x) 0 to 3.0% by weight of copper; and (xi) iron providing the balance of the alloy by weight

FIELD OF TIHE MVENTION

The present invention relates to an alloy composition suitable for use in glass making moulds and process for making same. In particular, this invention relates to a boron alloy mould which alleviates swabbing during the glass making process, without being limited thereto.

BACKGROUND OF THE INVENTION

The manufacture of glassware such as bottles, flasks, jars as used in foodstuffs and beverages involves the forming of molten glass in alloy mould assemblies at elevated temperatures, eg. 1200° C. Molten glass is dropped into a mould assembly which periodically opens and closes at high frequency rates.

Traditionally, blank mould assemblies have been made of grey cast iron which provides excellent foundry characteristics, is low-cost, is readily machinable and can take the high polish required for smoothly finished glassware. However due to its low hardness of about 20 Rockwell C, grey iron suffers from wear. The internal edges of the mould must be flame hardened to prevent edge wear and chipping. Further, it has a high thermal conductivity, which can result in uneven temperatures on the mould blank which in turn promotes uneven container wall thickness.

It is essential that grey iron blank moulds are regularly ‘swabbed’ with an oil-based lubricant to prevent glass adhering to it. The swabbing process is carried out manually by a line operator, who periodically swabs the blank mould using a cotton swab carrying the lubricant during the short time in which the mould is open. The swab must be extracted before the mould closes. In doing so, machinery must be halted and cooled to enable the swabbing process to occur. This down-time contributes to loss of productivity as well as incorporating hazardous and labour intensive work for the operator. Due to the extreme hazardous nature of this procedure for the line operator, it is anticipated that the swapping operations will be prevented by appropriate workplace health and safety regulations in the near future.

Reference may be made to U.S. Pat. No. 1,493,191 to de Golyer which refers to an alloy comprising 5 to 60% Cr, up to 15% B, up to 1.50% C and the balance being Fe. There also may be included 0 to 10% of Ca, W, Mo, Si, Al, Mn, Ni, Co, V, Ti, U and Zr. This alloy is used in a wide variety of articles of manufacture which include, for example, castings or forgings used as valves, engine parts, pumps and the like.

Australian Patent 693204 refers to an iron-chromium-boron alloy, suitable for the production of tools for the manufacture of glass articles and a tool made from the alloy, having a composition of from 1 to 20 wt. % Cr and from 0.5 to 3 wt % B. The composition only optionally contains C subject to C in excess of 1.0 wt % being bound by at least one strong carbide forming element in a carbide and/or carbo-boride phase, with the alloy otherwise only optionally including the at least one carbide forming element The composition also optionally contains one or more of Si up to 3 wt %, Al up to 0.2 wt %, Mn up to 2 wt %, Ni up to 3 wt %, Cu up to 3 wt. % and Mo up to 5 wt %. The balance is Fe.

The above references are typical of alloys that may be used generally in articles of manufacture such as in U.S. Pat. No. 1,493,191 or an alloy that is restricted to tools for the production of glass articles such as plungers, thimbles, guide plates and blow nozzles. However such prior art does not address or is specifically concerned with the problem of swabbing as discussed above.

OBJECT OF THE INVENTION

Accordingly, it is an object of the invention to provide an alloy composition which, when used in articles of manufacture including casting moulds, has an extended manufacturing life and alleviates the need for swabbing operations during glassware manufacture.

SUMMARY OF THE INVENTION

According to first aspect of the present invention there is provided an alloy comprising:

-   (i) 0.5-5% by weight of one or more carbide formers selected from     molybdenum, tungsten and vanadium; -   (ii) 0.3 to 1.5% by weight silicon; -   (iii) 5 to 40% by weight chromium; -   (iv) 0.5 to 5% by weight nickel; -   (v) 0.5 to 3.5% by weight boron; -   (vi) 0.1 to 0.5% by weight of carbon; and -   (vii) iron providing the balance of the alloy by weight apart from     optional elements that may be included in the alloy.

Preferably, the alloy comprises 0.3-1.5% by weight of one or more of the abovementioned carbide formers.

Preferably, the alloy comprises 0.5 to 1.5% by weight silicon. Preferably, the alloy comprises 5 to 20% by weight chromium. Preferably, the alloy comprises 1 to 1.5% by weight nickel. Preferably, the alloy comprises 1.8 to 2.2 % by weight boron. Preferably, the alloy comprises 0.18 to 0.3% by weight of carbon.

Suitably, the alloy further comprises 0 to 2% by weight of manganese as an optional element and more suitably, 0.4 to 1.5% of manganese.

Sulphur may be present also at 0.0 to 0.1% by weight as an optional element Phosphorus may be also present at 0.0 to 0.1% by weight as an optional element. Copper may be present at 0.0 to 3% by weight and preferably at 0.2 to 1.0% as an optional element.

Each element is chosen for its specific properties and their interaction, when formed, within the alloy lattice structure.

Boron contributes hardness to the alloy. It is practically insoluble in low temperature ferrite and high temperature austenite phases of iron, and therefore cannot affect the alloying or properties of the iron to any large degree.

Chromium, when added at a sufficiently high level, will provide oxidation and corrosion resistance due to the formation of a stable film of chromium oxide on the surface of the alloy. Usually more than 5% chromium in the matrix is required to provide these benefits, and a level of over 15% chromium is preferred in the alloy to provide oxidation and corrosion resistance and better wear properties at elevated temperatures due to secondary hardening.

Other alloying elements added to the material to improve matrix properties. Thus, silicon is added to shield the alloy during melting from excessive oxidation which can produce porous castings if the silicon content is too low.

The level of carbon is kept at low levels to provide a relatively tough martensite, but sufficiently high for it to initially form on air cooling of the alloy from high temperature.

Nickel is required to help the formation of martensite on cooling, as well as toughening the low carbon martensite as well.

Molybdenum as an example of a carbide former aids the formation of bainite on cooling of the alloy as well as the precipitating fine molybdenum secondary carbides at 490° C. and maintaining hardness at the working temperature of the blank mould of 450° C. to 480° C. This is shown in FIG. 3, which shows the increase in hardness followed by a softening by increased heating on heating the alloy at these temperatures. Similar comments apply to tungsten and vanadium.

Manganese as an optional element is present in the steel scrap used for melting the alloy. However manganese assists in matrix ductility, and shape control of manganese sulphide particles.

Sulphur and phosphorus are ubiquitous as impurities from the scrap and other ingredients at the indicated concentrations. They offer no assistance N hindrance provided they are present.

Copper as an optional element is added to produce an effect of extended hardenability that occurs with copper-boron alloy steels and irons. This can result in large sections being able to be through-hardened to bainite on air cooling from over 900° C. The blank moulds can have heavy sections of up to 75 mm and this extended hardenability will ensure that the entire section is fully transformed rather than just the outside layers.

The key advantage of the alloy as compared to that of traditional grey cast alloys in which moulds relate to obviating the need for swabbing. Specifically, the blank mould from the present alloy having the above essential elements (i), (ii), (iii), (iv), (v) and (vi) when coated with a ceramic spray containing boron nitride does not require swabbing after it is first installed on the blank mould support structure. Further, it does not require swabbing after the blank mould is taken from the support structure for cleaning and installed again and without any further coating being applied The elation of the swabbing procedure is an important improvement for the glass container industry.

According to a second aspect of the invention, there is provided a process of making a blank mould including the steps of:

-   -   (i) melting an alloy which is preferably an alloy of the first         aspect;     -   (ii) confirming that the alloy composition has a predetermined         ratio of elements by comparison with appropriate standards using         a technique selected from XRF (X-Ray Fluorescence) and AES         (Atomic Emission Spectroscopy) characterised in the case of         boron that a plurality of boron standards are used with the         lowest standard corresponding to 0.5% boron or less and the         highest boron standard corresponds to 3.5% boron or more;     -   (iii) casting the molten alloy from step (i) to form the blank         mould;     -   (iv) heating said casting to about 880-1000° C.;     -   (v) cooling said casting to a temperature of 200° C. or less         wherein the casting has a hardness of 50-60 Rockwell C;     -   (vi) softening the casting to a hardness required for machinery         by heating the casting to 700-750° C. for 34 hours to attain a         hardness of 30-38 Rockwell C;     -   (vii) re-hardening the casting by heating the casting to         880-1000° C. so that the casting has a hardness of 50-60         Rockwell C; and     -   (viii) reducing the hardness of the casting to 40-47 Rockwell C         by heating the casting to an optimum temperature or temperature         range within 480-700° C.

In relation to step (viii) the optimum temperature or temperature range can be determined having regard to a specific alloy composition by plotting temperature against hardness in terms of Rockwell C in relation to samples of the specific alloy composition which have already been subject to steps (i), (ii), (iii), (iv) and (v). This is shown in FIG. 3.

According to a third aspect of the present invention there is provided a blank mould made from the alloy of the first aspect and prepared by the process of the second aspect. The blank mould is suitable for manufacture of glass containers.

The blank mould can be machined and heat treated to give a final hardness of 40 to 47 Rockwell C. The blank mould is also polished in the mould cavity to give a very smooth surface that is not degraded at the relevant operating temperature by oxidation and whose hardness is kept at the desired level by secondary carbide precipitation, resulting in excellent life and performance of the mould without intermittent lubricant swabbing. The invention results in a marked improvement in performance of the blank mould.

For the purpose of the following discussion, the following definitions are used.

As used herein, “eutectic” phase is meant of maximum fusibility pertaining to an alloy or mixture which has the lowest melting point in which it is possible to obtain by the combination of the given components.

As used herein, “austenite” phase is meant as a solid solution in which gamma iron is the solvent, characterised by a face centred cubic crystal structure.

As used herein, “alpha ferrite” phase is meant as the form of iron that is stable below 910 degrees Centigrade for pure iron, and is characterised by a body centred cubic structure.

As used herein, “martensite ” phase is meant as an unstable constituent of rapidly cooled ferrous alloys that is formed by a diffusionless shear transformation into a body centred tetragonal crystal.

As used herein, “bainite” phase is meant as a retarded transformation product of undercooled austenite that forms by nucleation and growth of ferrite laths and fine carbides to form an acicular structure at temperatures between those of the temperature of formation of pearlite and martensite.

It will be appreciated that such definitions will be apparent to the person skilled in the art and may be obtained from the Metals Handbook latest edition published by the American Society for Metals.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the present invention may be more readily understood and placed into practical effect, preferred embodiments of the invention and prior art will be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1: Photo micrograph of a section of typical grey cast iron blank mould previously used for making beer bottles on an automatic machine. The microstructure consists of grey flakes of elemental graphite, randomly oriented in a matrix of eutectoid pearlite. Pearlite is a lamellar mixture of ferrite and iron carbide that precipitates from austenite at 723° C. and 0.8% carbon in pure iron-carbon alloys. The matrix contains considerable carbon.

FIG. 2: Photomicrograph of a section of the alloy of the present invention cut from a blank mould. The structure consists of light iron chromium boride eutectic plates in a darker matrix of tempered martensite and bainite.

FIG. 3: Secondary tempering curve for the alloy of the present invention. After being air cooled from 950° C., the alloy is tempered for three hours, and cooled by air quenching to room temperature after which the Rockwell C hardness is measured. There is a rise in hardness to a maximum hardness of 55 Rockwell C at 480° C., after which there is a decline in hardness. The peak represents the secondary hardening caused by the precipitation of fine chromium and molybdenum carbides in the martensite matrix.

FIG. 4: Exploded perspective view of a blank mould made from the alloy of the invention

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Generalised Method for the Manufacture of Alloys of the Invention

The eutectic iron chromium boron alloys require specific melting equipment and procedures in order to produce a sound casting. They are casting alloys and have to be melted in an electric induction furnace, preferably with a generator that produces a current with a frequency of at least 500 hz. This is necessary in order to melt the charge quickly under an hour to minimize oxidation losses of the high level of boron Furnaces that are used for iron and steel castings may have a current frequency of 150 hz or 50 hz and are unable to induce sufficient current in the charge to melt the alloy quickly enough. Furnaces using fuel such as gas or oil can not be used, as they will result in extensive and uneven oxidation losses of the boron and chromium, which in turn will generate considerable fluid slag that is difficult to remove fully and which is likely to enter the mould with the molten metal and produce a faulty casting. Electric arc furnaces are not suitable because their electrodes are made of graphite, and the carbon arc will result in carbon pickup in the molten metal, which will render the castings very brittle and unsuitable.

An induction furnace suitable for melting the alloy for a production foundry would preferably be over 200 kg capacity and up to 1500 kg capacity, though smaller and larger furnaces can be used. At the start of a melting campaign, the base of the furnace is rammed in using a dry refractory lining, which consists of a range of particle sizes of the chosen ceramic (e.g. silica) from 5 mm down to dust The size grading is carefully designed so that the lining will achieve maximum packing density when the lining is rammed into place initially using pencil pointed ramming tools, then a flat rammer, until the base is solid and produces a ringing tone when struck with the flat rammer. The dry ceramic lining material should be previously mixed in a suitable mixer to ensure that the size grading of the ceramic particles are evenly mixed. Dry ceramic linings are subject to size segregation during transport, and many are transported over long distances where the fine dust sized particles can segregate to the bottom of the container.

Once the base is rammed, a cylindrical steel former with a flat bottom and tapered to the sides of the cylinder is positioned centrally in the furnace so that there is between 50 mm to 150 mm space between the former and the coil grouting. 50 mm is used for small furnaces and 150 mm for large furnaces. The furnace manufacturer will normally recommend the space between the former and the coil grouting. Once the steel former whose external surface has been previously been cleaned by shot blasting, is correctly positioned, more of the dry lining is placed between the former and the coil, evenly round the diameter of the former in layers about 100 to 150 mm thick, and rammed to maximum density. This process is continued until the dry lining is rammed up to within about 100 mm of the top of the furnace. Then a plastic refractory material is rammed into position. This ‘cap’ serves as seal to keep in the dry lining and to act as a mechanical shield. The furnace is the ready to be charged to produce the initial melt for the lining. For large furnaces, a special air operated vibrator attached to the former can vibrate the steel former so that the dry lining will compact This can result in considerable time savings. Hand ramming of the base of large furnaces is still preferred.

The ice assembly is typically engineered so that the entire furnace, together with electric leads and hydraulic hoses, will tilt about an axis at the lip of the furnace so that all the molten metal will flow evenly from the furnace into a pouring ladle, which can then be used to pour the moulds.

First Charge Melting

The steel former is consumed during the first melt for any lining, and acts as a sintering agent for the dry ceramic lining. If done correctly, the lining will develop a solid sintered skin on the external surface, with dry lining behind the sintered layer. For the first melt the furnace charge is heated slowly to red heat, so that the steel former is evenly heated to allow the lining skin to develop. Then the charge is heated more rapidly until the charge is molten, The melt is then heated to about 100 degrees Centigrade above the normal maximum temperature and held for some 30 minutes, to fully frit the skin of the lining to a glass like state. After the first melt is poured, the furnace is now ready for production of more melts. The lining now has a flitted skin that holds in the dry powder behind it If a fine crack should develop into a larger one, any molten metal that went through the crack would come in contact with the dry powder and stop. As the lining wears out, the sintered skin flits into the dry lining until there is only about 10 mm of dry powder left. At this stage it is recommended that the lining should be knocked out and a new lining installed with another sacrificial steel former. During a furnace melting campaign, near the half way point, the cap should be removed, and a thin steel rod pushed into the dry lining to determine how much dry powder is let, and if need be to top up the dry powder with fresh powder, as some may have settled during operation and vibration of the furnace. A new cap is then installed.

It is essential during the melting process, that there is still some dry powder between the lining and the coil. If not, then a large crack can let molten metal penetrate through the sintered lining to the water-cooled copper coil carrying the current. The coil can be breached and the resultant damage can be dangerous and catastrophic.

There are a number of suitable dry ceramic lining materials that are available to the foundry. The most common for irons and lower melting point alloys are based on silica and are called acid linings. They can be used for irons and steels up to 1600° C. and are suitable for the alloy of the invention. Other ceramic linings are based on magnesite or magnesite with 20% alumina which are used for cast irons and steels. These linings are not suitable for the boron alloy, since the slag from the melting of these alloys is acidic in nature due to the boron oxide in the slag, and this acid slag will react with the basic magnesite lining and cause excessive wear. In contrast to normal cast irons and steels, which can use any type of lining, the alloy of the invention is best melted in an induction furnace lined with silica.

Alloy Melting

The alloy is ferrous and requires ferrous-based charge components, or those that can dissolve in molten iron. Representative charge materials are set out below, which may comprise (a) 600-680 kg and more preferably 640 kg of low carbon steel scrap purchased from a scrap merchant; (b) 80-120 kg of ferro-boron containing 20% boron with the remainder iron and more preferably 100 kg of ferro-boron; (c) 200-230 kg of ferro-chromium containing 70% chromium and the balance iron and more preferably 214 kg of ferro-chromium; (d) 12-18 kg of nickel and more preferably 15 kg of nickel; (e) 24 kg of copper and more preferably 3.5 kg of copper if required, (f) 6-10 kg of ferro-molybdenum and more preferably 8 kg of ferro-molybdenum; (g) 5-7 kg of ferro-manganese containing 75% manganese and a maximum amount of 0.08% carbon and more preferably 6 kg of ferro-manganese if required; (11-15 kg of ferro-silicon containing 75% silicon and more preferably 13.3 kg of ferro-silicon and (i) 1.5-2.0 kg of carbon and more preferably 1.8 kg of carbon.

The amounts used in components (a), (b), (c), (d), (e), (fl, (g), (h) and (i) are based on 100 kg of charge. It will also be appreciated that ferro-vanadium containing 75% vanadium and/or ferro-tungsten containing 70% tungsten may be used in lieu of ferro-molybdenum.

With knowledge of the composition of the ingredients, a charge can be calculated that will make a melt on the low side of the required composition.

Part of the steel scrap charge is added to the base of the furnace crucible. The scrap should be clean, and having the largest piece no longer than one third the diameter of the crucible to minimize hang-ups. The ferro boron is then added to the steel on the bottom of the furnace, then the ferro chromium and then more of the steel scrap. The power is then turned on to heat the charge quickly, and melting will initiate at the bottom of the furnace. As the charge melts more scrap and the rest of the alloying elements is added until the furnace is full. The temperature of the molten metal is checked with an immersion thermocouple or other suitable instrument then held and controlled at 1350° C. At this point a sample of the molten alloy is taken with a small spoon and poured into a chill mould in a copper block to provide a disc about 50 mm diameter and 5 mm thick. One side of the disc is ground on an abrasive wheel to provide a clean surface for chemical analysis by an optical emission spectrograph The final composition of the melt can then be adjusted to bring the melt to the required composition.

The adjusted metal is held at a temperature to suit the section thickness of the casting between 1380° C. and 1450° C. The molten metal should not be heated to over 1550° C. as it will produce copious fumes of boron oxide, an irritant to mucous membranes.

Before the metal is poured from the furnace, the power is switched off and any slag allowed to float to the surface. The slag from the molten alloy is very fluid and must be removed by adding slag coagulants to the surface of the metal and skimmed off with a steel paddle. The temperature of the liquid metal should be checked again and the metal can be poured into a preheated ladle if the temperature is correct. The castings can then be poured immediately from the ladle. Any slag that appears on the surface of the metal in the ladle can be prevented from entering the casting mould with a flat steel skimming bar held near the lip of the ladle.

Segregation of Alloy Runners and Scrap Spectrographic Analysis of High Boron Alloys

In order to analyse the actual chemical composition of the alloy as it is being produced in the foundry, variations to the standard Atomic Emission Spectroscopy (AES) method are employed. Suitably also, is the X-Ray Fluorescence Spectroscopy (XRF) technique.

Both techniques utilise elemental internal instrument standards in which to quantify the amount of each element present. While known AES or XRF elemental standards may be employed for steel alloys containing low B concentrations (ca. 0.001-0.006% B), the present invention includes the use of new B standards so as to accurately measure the actual B levels for highly enriched B alloys of up to 500 times that of conventional steel alloys, i.e. ca. 2 to 5% B.

In order for this high level of boron to be measured accurately, it is imperative that the spectrograph machine is calibrated on a boron line that is different to the boron line used for the analysis of the low concentrations used in traditional steels. The spectrograph is operated in the usual manner known to a skilled person. Once the new boron line is chosen, (182.64 nm) then standard alloys of known composition and levels of boron from low levels of 0.19% B to 3% B are measured by the spectrograph, and a calibration line is calculated. The calibration line can now be used to measure the boron level in an unknown sample. Stability of the boron line must be calibrated each day by use of standards of a known boron level to correct for spectrograph drift due to slight changes in temperature and mechanical stability despite being housed in temperature controlled rooms.

A typical AES analysis of secondary standard B 2.5 showing the results of two bums (analysis events) on the standard and the values of the concentration ranges of each element measured for an alloy, and the spectral lines used for each element is shown in Table 1. Boron is calibrated and analysed using the line at 182.64 nanometres.

Post Casting Treatment of the Alloys

After casting the alloy into moulds and allowing the moulds to cool, the castings can be knocked out for subsequent treatment. The treatment involves separating the casting from the runners and feeders that are attached to the casting. The runners allow the molten metal to be poured into a cup on the surface of the mould, and then to flow direly into the mould cavity. The feeders are excess molten metal usually placed on top of the mould cavity that allows it to act as a reservoir of molten metal as the casting cools and freezes, contracting in volume as it does so. The feeder makes up for that shrinkage. With grey cast irons and white irons, the runners and feeders are knocked off using hammers, which often leaves an area that must be ground flat with a grinding wheel. This process is slow and expensive. Sometimes the breaking off procedure will result in the casting being damaged by “breaking in” which results in a rejected casting. With the boron alloys, the runners can be cut off with an abrasive cut-off wheel almost flush with the casting surface.

Heat Treatment of Blank Mould Castings

After being fettled to remove the runners and risers, the castings are homogenized and softened to reduce the hardness from 50-60 and more preferably 55 Rockwell C in the as cast condition, to 30-38 and more preferably 35 Rockwell C to allow for machining and to remove any retained austenite which is deleterious to machineability that may occur in the microstructure. This is accomplished by initially heating the castings to 880° C. to 1000° C. and more preferably 900-950° C. to austenitise the matrix, followed by cooling to room temperature in air or any other temperature below 200° C. The carbon content of the matrix at this temperature is constant as there are no eutectic carbides or graphite to dissolve in the matrix. Further, boron does not dissolve in the matrix and so the matrix composition is unchanged. On cooling, the matrix now transforms to martensite and some bainite. The eutectic borides remain unchanged. The hardness of the alloy at this point is about 50-60 and more preferably 55 Rockwell C.

The casting can now be softened to the hardness required for machining by tempering the alloy by heating in air to 700 to 750° C. for 34 hours. This sub-critical annealing treatment will soften the casting to 30-38 Rockwell C and more preferably 32-35 Rockwell C. The casting is now ready for any machining operation that is needed.

Once the blank mould is machined and polished, it is rehardened by heating the blank mould in a vacuum heat treatment furnace at 880° C. to 1000° C. for 1-3 hours and cooled in the vacuum furnace, e.g. by a nitrogen gas quench to just above room temperature. The vacuum furnace is used to preserve the integrity of the machined surface. The hardness of the blank mould is now 50-60 Rockwell C and more preferably 55 Rockwell C.

However, this high degree of hardness is unsuitable as damage to other machinable parts, including loose tools, occurs.

To address this limitation, this invention provides a process whereby the hardness may be adjusted to suit that which is required in the working environment. The hardness of the blank mould may be reduced to 40-47 Rockwell C and more preferably 42-45 Rockwell C by a secondary tempering or hardening step. The present inventor has determined that by selecting the optimum temperature, the hardness may be tailored to suit specific applications. In this instance, the manufacturing of glass from such blank moulds occurs at 450 to 480° C. By using the tempering curve of FIG. 3, the desired hardness may be selected by determining the temperature at which the article of manufacture is tempered.

This secondary hardening is due to the selective precipitation of metal carbides in the martensite lattice structure at various temperatures. For example, Cr₇C₃ precipitates as fine nanoparticles in crystalline form at 500° C., whereas Mo₂C precipitates at 550° C. The greater the fine metal precipitate thoughout the lattice, the greater the hardness. However, at temperatures above 550° C., the nanoparticles begin to coalesce and align through the matrix. The crystallographic realignment reduces the stress within the matrix, and in doing so, softens the metal alloy. Thus tailoring the temperature to correlate with the alloy composition is critical to achieve the desired degree of hardness.

The extremely slow nature of the precipitation of carbides during tempering below the secondary hardness peak is of critical importance for the operating of the invention as blank moulds as they operate at 450° C. to 480° C. and do not soften appreciably after many weeks on the glass moulding machine.

The tempering temperature for the blank mould is chosen at 550-630° C., past the hardness peak having regard to an alloy having the composition set out in Example 1, so that when the blank mould is installed on the operating glass container machine which operates at about 480° C., the fine alloy carbides in the matrix which have already enlarged at the tempering temperature of 550-630° C., will not enlarge any further, due to extremely slow diffusion of iron in the high chromium content in the matrix, and the hardness of the blank mould will not drop. The hardness of the blank mould will therefore remain steady over a long period of time, and the blank mould will show exceptional wear at the elevated temperature on the operating machinery.

If the secondary hardening temperature range is not determined according to the curve of FIG. 3, the behaviour or characteristics of the alloy will not be reproducible to ensure appropriate operational longevity. This means that the alloy may not be suitable for commercial use.

For conventional grey cast iron mould castings having the structure shown in FIG. 1, the mould cavity is hardened on the edge to improve the resistance of the mould to chipping on the edge. Any edge chipping would leave a defect lump on the side of the glass paracen which would result in the rejection of the container and replacement of that particular mould, and its final rejection if the broken area cannot be repaired.

It will be appreciated by a skilled person that the present alloy does not require the edge hardening treatment, as it is sufficiently hard after machining, hardening and tempering for direct service.

Blank mould preparation for glass container production machines Before the blank mould is installed on the glass moulding machine, the polished surface of the mould cavity is sprayed with thin film of a commercially available ceramic coating (eg. Certek 700 or SG 7500 ABN) containing boron nitride in a liquid carrier. The blank mould is then heated to temperatures above the operating temperature of the mould to set the conic coating, usually about 250° C. The blank mould is then installed on the machine.

Unlike a would of the present invention made from an alloy having the structure shown in FIG. 2, the grey cast iron mould must be regularly swabbed with a liquid lubricant to prevent the molten glass from adhering to the mould surface. After the mould surface is swabbed, the next two or three containers from the mould can be rejected. The swabbing procedure has previously occurred while the forming machine was operating, however accidental injury to the machine operator ensued. Presently, the machine is stopped while the swabbing is done. This results in interruptions to the production of glass containers and cooling of the moulds and further complications arising from this cooling.

It will be appreciated that until now, known alloy compositions used in manufacturing glassware in particular have achieved only moderate wear resistance properties, being prone to thermal cracking and oxidation in particular. The alloy of this present invention has surprisingly high ability to endure high frequency cycling and thermal stresses due to its tailored hardness when used in an article of manufacture such as glassware mould casts.

FIG. 4 shows a blank mould 10 having an internal bore 11 which forms the parison or bottle former having cooling fins 12 on an external surface 13 as well as a hollow external component 14 forming a cooling chamber (not shown). There is also provided securing plate 15 having apertures 19 for fasteners (not shown) attaching component 14 to inner component 16 and locating flanges 17 for locating the blank mould 10 onto the glass forming machine (not shown). There is also shown guide structure 18 for plungers and other loose tools (not shown) involved in the forming operation of the invention. The blank mould 10 is formed from the alloy or at least the internal component 16 is formed from the alloy of the invention.

EXAMPLES Example 1 Alloy Composition

The alloy is ferrous and requires ferrous-based charge components, or those that can dissolve in molten iron. Percentages are expressed in percentage by weight as are all percentages herein unless expressly specified otherwise. A suitable final composition of the alloy of the invention may be as follows: Carbon 0.22% Silicon 0.88% Manganese 0.77% Phosphorus 0.05% Sulphur 0.04% Nickel 1.48% Chromium 16.5% Molybdenum 0.55% Copper 0.35% Boron 1.96% Iron Balance

Example 2

The curve of FIG. 3 was obtained by cutting a test bar casting of the alloy of Example 1 of dimensions 30 mm diameter and 300 mm long into ten cylindrical pieces each of 30 mm diameter and 15 mm thickness or length which each weighed about 200 g. Each piece was placed into a furnace at room temperature and heated to 950° C. for an hour. The red hot pieces were then taken out of the furnace and were each cooled to room temperature. Then each piece was placed into preheated furnaces at 200° C., 250° C., 300° C., 350° C., 400° C., 450° C., 500° C., 550° C., 600° C., 650° C. and 700° C. for three hours. Then each piece which was red hot was quenched with cold water back to room temperature. The hardness of each of the samples was then measured on a previously calibrated Rockwell Hardness machine on the Rockwell C scale and the results shown in FIG. 3.

Without wishing to be bound by any particular theory, the present invention reasons that there is a strong attraction between the boron nitride in the ceramic coating and the iron chromium boride eutectic particles on the surface of the boron alloy blank mould. This is supported by the fact that even after the boron alloy mould is removed from the machine after producing glass containers and then cleaned, it does not require recoating with the ceramic and does not require swabbing after being replaced on the machine, This is contrary to the performance of traditional grey cast iron blank mould which requires swabbing on a regular basis at all times.

It will be appreciated by the skilled person that the present invention is not limited to the embodiments described in detail herein and that a variety of other embodiments may be contemplated which are nevertheless consistent with the broad spirit and scope of the invention. TABLE 1 Chrom- and Chrom-Nickel Steel Boron Sample ID B2.5 C Si Mn P S Cr Mo Ni Al Co 1 0.262 0.861 0.882 0.0209 0.0155 16.42 0.173 1.88 0.0597 .00900 2 0.264 0.873 0.887 0.0188 0.0128 16.42 0.457 1.88 0.0609 .00964 Cu Nb Ti V W Pb Sn B Fe 1 0.104 0.0134 <.00050 0.0286 <.00690 <.00120 0.0102 2.30 <76.65 2 0.105 0.0138 <.00050 0.0282 <.00690 <.00120 .00861 2.23 <76.73 Symbol Element Reference Cone. Range Wavelength Source cond. C C Fe1 .00200-2.20  % 193.09 nm Spark Si Si Fe3 .00440-4.00  % 251.61 nm Spark Mn Mn Fe2 .00050-8.50  % 293.31 nm Spark P P .00060-0.120 % 178.29 nm Spark S S .00030-0.120 % 180.73 nm Spark Cr2 Cr Fe4 .00560-55.00 % 298.92 nm Spark Mo Mo Fe4 .00180-18.00 % 281.61 nm Spark Ni Ni Fe5 .00100-6.00  % 352.45 nm Spark Ni2 Ni Fe2  6.00-85.00 % 376.95 nm Spark Al Al Fe3 .00070-0.250 % 394.40 nm Spark Co Co Fe3 .00130-0.600 % 345.35 nm Spark Cu Cu Fe5 .00440-8.00  % 510.55 nm Spark Nb Nb Fe4 .00160-1.60  % 319.50 nm Spark Ti Ti Fe2 .00050-3.60  % 337.28 nm Spark V V Fe2 .00060-0.600 % 311.07 nm Spark W W Fe5 .00690-0.250 % 400.88 nm Spark Pb Pb  .00120-0.0300 % 405.78 nm Spark Sn Sn .00010-0.200 % 189.99 nm Spark B B Fe1 .00010-2.60  % 182.64 nm Spark Fe1 Fe  1200-7200 187.75 nm Spark Fe2 Fe  6000-26500 273.07 nm Spark Fe3 Fe  1000-4000 360.88 nm Spark Fe4 Fe  1000-4000 273.07 nm Spark Fe5 Fe  1000-5000 360.88 nm Spark 

1. An alloy comprising: (i) 0.5-5% by weight of one or more carbide formers selected from Molybdenum, tungsten and vanadium; (ii) 0.3 to 1.5% by weight silicon; (iii) 5 to 40% by weight chromium; (iv) 0.5 to 5% by weight nickel; (v) 0.5 to 3.5% by weight boron; (vi) 0.1 to 0.5% by weight of carbon; (vii) 0 to 2% by weight of manganese; (viii) 0 to 0.1% by weight of sulphur; (ix) 0 to 0.1% by weight of phosphorous; (x) 0 to 3.0% by weight of copper; and (xi) iron providing the balance of the alloy by weight.
 2. An alloy according to claim 1 wherein said alloy comprises 0.3-1.5% by weight of said one or more carbide formers.
 3. An alloy according to claim 1 wherein said alloy comprises 0.5 to 1.5% by weight silicon.
 4. An alloy according to claim 1 wherein said alloy comprises 5 to 20% by weight chromium.
 5. An alloy according to claim 1 wherein said alloy comprises 1 to 1.5% by weight nickel.
 6. An alloy according to claim 1 wherein said alloy comprises 1.8 to 2.2% by weight boron.
 7. An alloy according to claim 1 wherein said alloy comprises 0.18 to 0.3% by weight of carbon.
 8. An alloy according to claim I wherein said alloy comprises 0.4 to 1.5% by weight of manganese.
 9. An alloy according to claim 1 wherein said alloy comprises 0.2 to 1.0% by weight of copper.
 10. A process of making a blank mould including the step of: (i) melting an alloy which is preferably an alloy of the first aspect; (ii) confirming that the alloy composition has a predetermined ratio of elements by comparison with appropriate standards using a technique selected from XRF (X-Ray Fluorescence) and AES (Atomic Emission Spectroscopy) characterised in the case of boron that a plurality of boron standards are used with the lowest standard corresponding to 0.5% boron or less and the highest boron standard corresponds to 3.5% boron or more; (iii) casting the molten alloy from step (i) to form the blank mould; (iv) heating said casting to about 880-1000° C.; (v) cooling said casting to a temperature of 200° C. or less wherein the casting has a hardness of 50-60 Rockwell C; (vi) softening the casting to a hardness required for machinery by heating the casting to 700-750° C. for 34 hours to attain a hardness of 30-38 Rockwell C; (vii) re-hardening the casting by heating the casting to 880-1000° C. so that the casting has a hardness of 50-60 Rockwell C; and (viii) reducing the hardness of the casting to 40-47 Rockwell C by heating the casting to an optimum temperature range within 480-700° C.
 11. A process as claimed in claim 10 wherein in step (i) a charge material is discharged to a furnace having (a) 600-680 kg of steel scrap; (b) 80-120 kg of ferro-boron; (c) 200-230 kg of fee chromium; (d) 12-18 kg of nickel; (e) 6-10 kg of ferro-molybdenum, and ferro-tungsten or ferro-vanadium, (f) 11-15kg of ferro-silicon and (g) 1.5-2.0 kg of carbon, wherein amounts (a), (b), (c), (d) and (e) are based on 1000 kg of charge material.
 12. A process as claimed in claim 11 wherein the charge material contains 640 kg of steel scrap, 100 kg of ferro-boron, 214 kg of ferro-chromium, 15 kg of nickel, 8 kg of ferro-molybdenum, ferro-tungsten or ferro-vanadium, 13.3 kg of ferro-silicon and 1.8 kg of carbon.
 13. A process as claimed in claim 11 wherein the charge material also contains 24 kg of copper and 5-7 kg of ferro-manganese.
 14. A process as claimed in claim 13 wherein the charge material contains 6 kg of ferro-manganese and 3.5 kg of copper.
 15. A process as claimed in claim 10 wherein step (viii) is carried out by heating the casting to an optimum temperature or temperature range within 480-700° C. which optimum temperature or temperature range can be determined having regard to a specific alloy composition by plotting temperature against hardness in terms of Rockwell C in relation to samples of the specific alloy composition which have already been subject to steps (i), (ii), (iii), (iv) and (v).
 16. A process as claimed in claim 10 wherein in step (iv) the casting is heated to 900-950° C.
 17. A process as claimed in claim 10 wherein in step (v) the casting is cooled to room temperature.
 18. A process as claimed in claim 10 wherein in step (v) the casting has a hardness of 55 Rockwell C.
 19. A process as claimed in claim 10 wherein in step (vi) the casting has a hardness of 32-35 Rockwell C.
 20. A process as claimed in claim 10 wherein in step (vii) the casting is heated to 900-950° C.
 21. A process as claimed in claim 10 wherein in step (vii) the casting has a hardness of 55 Rockwell C.
 22. A process as claimed in claim 10 wherein after step (viii) the hardness of the casting is 42-45 Rockwell C. 